1. Field of the Invention
The present invention relates, in general to an antenna, more particularly to a physically small surface mount type antenna.
2. Description of the Related Art
The development of wireless local area network (wireless LAN) technologies increases demand for physically small antennas. An instrument including an antenna that constitutes a wireless LAN system is often required to be small, and this heightens the need for physically small antennas. Physically small antennas suitable for wireless LAN systems are disclosed in Japanese Open Laid Patent Application (Jp-A-Heisei 8-84019, Jp-A-Heisei 8-97626, Jp-A-Heisei 9-74308, Jp-A-Heisei 9-74309, and Jp-A-Heisei 10-41736) and Japanese Registered Utility Model Gazette (Jp-U 3041690). “Antennas and Radio Propagation”, which is published by Corona Publishing Co., Ltd. in Japan, discloses in pages 69 and 70 that top-loading effectively reduces the size of the antenna.
An antenna used in a wireless LAN technology is desired to meet several requirements. Firstly, an antenna is desirably designed to have a wider bandwidth. In recent years, many countries tend to allocate wider frequency ranges to wireless LAN systems. This situation heightens the need for a physically small antenna that has a wider bandwidth.
Second, a cost of an antenna is desirably reduced. The cost of manufacture is one of the important factors to determine competitiveness of manufacturers of antennas.
Third, an antenna is desirably easy to adjust its characteristics, such as the input impedance and the resonance frequency. The fabrication process of an instrument with an antenna usually includes adjustment of the characteristics of the antenna. The easy adjustment of the characteristics is quite advantageous to improve efficiency of the fabrication process.
Fourth, an antenna is desirably designed to be suitable for automatic surface mounting, because the use of the automatic surface mounting effectively reduces the cost needed for mounting an antenna onto a printed circuit board. The automatic surface mounting includes automatic positioning and automatic soldering. Thus, it would be advantageous if the antenna has a structure suitable for automatic positioning and automatic soldering.
Fifth, an antenna desirably has a structure that facilitates a visual inspection to confirm the connection between the antenna and the printed circuit board.